Engineering plastics such as polyacetal resins; aromatic thermoplastic polyesters such as polyethylene terephthalate and polybutylene terephthalate; thermoplastic polyamides such as nylon 6 and nylon 6,6; and polyesteramides which are copolymers of the abovementioned polymers are widely used as resins due to their excellent tensile strength, tear strength, resilience cold resistance and bending resistance. Attempts have been made, however, to add various substances to these resins to form a composition having modified properties and improved functions. It is known, for example, that when a solid filler is employed, coupling agents and some surfactants are also needed in order to improve the compatibility of the filler's surface with the matrix resin so as to obtain a homogeneous dispersion of the former in the latter
However, when the modifiers are resins or liquid substances having solubility parameters .delta. which are different from one another, their compatibility with one another is sufficiently poor so that homogeneous dispersions cannot be obtained in many cases.
In such a situation, conventional coupling agents are useless. In addition, ordinary surfactants have poor heat stability and are therefore unsuitable for use as an additive in engineering plastics, which necessitate processing at high temperatures. Particularly, when an oily substance or the like is to be dispersed in a resin, it cannot be used in large amounts since it would otherwise separate from the resin (i.e., "bleed"). Even when an oily substance is used in small amounts, problems ensue such as the inability to form homogeneous dispersions, poor product appearance non-uniform physical properties, reduced mechanical strength. Moreover, when polymers are blended together, problems similar to those encountered with use of oily substance ensue, such as non-uniform dispersions creation of a surface peeling phenomenon, and non-uniform mechanical strengths.
Techniques to solve these problems have been proposed. For one example, technique involves using a block copolymer having a segment which is the same as that of the substance to be dispersed in the matrix resin. Another technique involves using components that may be chemically bonded together by, for example, an exchange reaction, so as to improve the components surface affinities. However, these techniques lack versatility because the number of suitable components that may be employed is limited. That is, a number of available components cannot be used according to these techniques and thus different formulations are necessary depending upon the components that are employed.
An object of the present invention is to provide a thermoplastic resin composition exhibiting increased toughness and excellent abrasion resistance, which is prepared by melt-blending so as to obtain a homogeneous dispersion without causing bleeding and/or without reducing the composition's mechanical and physical properties.
The present invention is based upon the discovery that specified siloxane copolymers (to be discussed in detail below) are not decomposed at high temperatures, and exhibit a desirable surface-activating effect so that they can be used as a compatibilizing agent for a number of components to be incorporated into a resin composition. These siloxane copolymers thus form a homogeneous dispersion even when components are used having significantly different solubility parameters as compared to the solubility parameter of the siloxane copolymers.